make_ext4fs has moved to build/target/core.mk
There's no need to add make_ext4fs to each device since it's in
build/target/core.mk since commit
720479ea7e6307648c56f61d82ac12d65f218dda
Bug: 6960586
Change-Id: I916b06e9d696764d1944d3c911ab75f4ef34fb7d